WO2024167672A1 - Lightweight concrete made via redox reaction using carbon aggregate - Google Patents

Abstract

A composition for a low cost, lightweight carbon aggregate concrete made from coal using a reduction/oxidation reaction and a method for making lightweight concrete utilizing lightweight carbon aggregate in a reduction/oxidation reaction is described.

Description

LIGHTWEIGHT CONCRETE MADE VIA REDOX REACTION USING CARBON

AGGREGATE

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present invention claims priority to U. S . Provisional Patent Application No. 63/444,121, filed February 8, 2023: and is related to PCT/US2021/031897 filed May 12. 2021, and US App. No. 17/920,986 filed October 24, 2022 as a National Phase entry of PCT/US2021/031897, now issued as US Patent No. 11,685,690 on June 27, 2023.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0002] This invention was made with government support under DE-FE0031992 awarded by the Department of Energy. The government has certain rights in the invention.

FIELD OF THE DISCLOSURE

[0003] The present invention is directed to a lightweight carbon aggregate concrete composition produced using a reduction/oxidation reaction with lightweight vitreous carbon aggregate from coal at atmospheric pressure.

BACKGROUND OF THE DISCLOSURE

[0004] About 10 billion tons of concrete is produced every year, which is more than one ton per person on the planet; it is the second most used material next to water.

Approximately 70% of the volume of concrete is composed of aggregate, which puts the usage volumes of aggregate on the scale of billions of tons per year.

[0005] Concrete makes up a large part of the infrastructure of the United States, which is under considerable strain. Improved concrete designs that enhance the life of structures that make up our infrastructure are required. The spectrum of concrete products is quite broad, and a wide variety of designs exist. One efficient and wcll-cnginccrcd product is Structural Lightweight Concrete, which is a material that uses lightweight aggregate to achieve certain property improvements over those of heavier, more conventional concrete designs. Examples include better thermal properties, better fire ratings, reduced autogenous shrinkage, excellent freezing and thawing durability, improved contact zone between aggregate and cement matrix, less micro-cracking as a result of better elastic compatibility, more blast resistance, better shock and sound absorption, less cracking, improved skid resistance, and easier placement via concrete pumping. Examples of specific applications include heat insulation on roofs, insulating water pipes, construction of partition walls and panel walls in frame structures, general insulation of walls, and surface rendering for external walls of small houses.

[0006] Aggregates, which are essential ingredients of concrete, may be derived from natural sources with minimal processing or from naturally occurring materials that are heat treated. Aggregates may also be synthetic. Aggregates from natural sources, such as quarries, pits in ground, and riverbeds, for example, are generally composed of rock fragments, gravel, stone, and sand, which may be crushed, washed, and sized for use, as needed. Natural materials that may be used to form aggregates include clay, shale, and slate, which are pyroprocessed, causing expansion of the material. OPTIROC and LECA are examples of commercially available expanded clay aggregates, for example. Synthetic aggregates may comprise industrial byproducts, which may be waste materials. LYTAG. for example, is a commercially available sintered aggregate comprising pulverized fuel ash (“PF A”), also known as fly ash. PFA is the residual particulate oxide material left over from the combustion of coal in power plants, for example.

[0007] Aggregates may be lightweight or normal weight. Lightweight aggregates (“LWAs”) have a particle density of less than 2.0 g/cm³ or a dry loose bulk density of less than 1.1 g/cm³, as defined in ASTM specification C330. Normal weight aggregates from gravel, sand, and crushed stone, for example, generally have bulk specific gravities of from about 2.4 to about 2.9 g/cm³ (both oven-dry and saturated-surface-dry), and bulk densities of up to about 1.7 g/cm³. High quality LWAs have a strong, but low density and porous core of uniform structural strength. LWAs may also have a dense, continuous, relatively impermeable surface layer to inhibit water absorption. They are physically stable, durable, and environmentally inert. LWAs may be designed to have a nearly spherical shape to improve the rheology and flow of fresh concrete, or more angular shape to provide better strength after the concrete is properly compacted. The surface of the LWA should also provide good adherence to concrete paste. Suitable sizes for incorporation in concrete range from about 0.5 to 25 nun, depending on the application, or 2.36 mm to 9.5 mm for coarse aggregates, in accordance with ASTM Specification C330. Smaller, fine aggregates, which are a byproduct of LWA production, may also be used to replace sand in concrete, for example. For use in concrete, LWAs should have a sufficient crush strength and resistance to fragmentation so that the resulting concrete has a strength of greater than 10 MPa and a dry density in a range of about 1.5 g/cm³ to about 2.0 g/cm³. Concrete containing LWAs (“LWA concrete”) may also have a density as low as about 300 kg/m³. [0008] While LWA concrete may be 20-30% lighter than conventional concrete, it may be just as strong. Even when it is not as strong as conventional concrete, the LWA concrete may have reduced structural dead loads enabling the use of longer spans, narrower cross - sections, and reduced reinforcement in structures. The lower weight of the LWA concrete facilitates handling and reduces transport, equipment, and manpower costs. LWA concrete may be particularly useful in construction slabs in high rise buildings and in concrete arch bridges, for example. LWA concrete may also have improved insulating properties, freezethaw performance, fire resistance, and sound reduction. LWAs can also be used in the construction of other structures, in highways, and as soil fillers, for example.

[0009] Quarrying is tire largest source of aggregates by volume in most countries. Despite tire many advantages of LWAs, aggregate extraction is complicated by environmental and legal issues, availability, transportation, and other costs, for example.

[0010] One important additional property of lightweight aggregate is its ability to hold water, which enables internal curing, a process by which tire hydration of cement on the inside of the concrete can continue at later times using water that is not a part of the original mixing water, ultimately achieving a greater extent of hydration and improved properties. The goal of internal curing is to maximize hydration, essentially ensure as much of the reactants as possible are converted to hydrates and minimize self-desiccation when low watcr-to-ccmcnt ratios arc utilized, which in turn minimizes tire accompanying stresses that may produce early-age cracking. An important point when utilizing internal curing is that the water within tire aggregate must not release early and combine with the mix water of the fresh concrete, else the water-to-cement ratio of the product will be adversely affected.

[0011] The lightweight aggregate used in a concrete design must be engineered to manage: 1) the amount of internal curing water introduced to the concrete after set, 2) the location of curing water in the matrix, and 3) the proper sizes of aggregates to meet the overall particle size demands of tire mix design. Internal curing has been employed in a variety of concrete mixtures for diverse applications including bridge decks, pavements, transit yards, and water tanks: hundreds of thousands of cubic meters have been successfully placed throughout the U.S.

[0012] The water content of lightweight aggregates such as pumice, expanded clay, or expanded shale can be difficult to manage. Water readily wets the material and can easily flow into and out of the aggregate. Thus, piles of aggregate must be constantly monitored and maintained with water sprinklers and turned regularly using large equipment. V ariation in water content can impact the water-to-cement ratio of tire concrete mix, thereby adversely impacting properties. Water permeating through the concrete microstructure after hardening will tend to flow easily through any open porosity within the aggregate.

[0013] Given all these materials contain silica, there is potential for damage through alkali silica reaction.

[0014] Pumice has a very low density, but can be highly irregular in shape, very friable, and the distribution of particles can be highly variable. It tends to breakdown during the concrete mixing process, changing the overall particle size distribution.

[0015] Prior art methods and materials use fly ash (or coal ash) to make their aggregate. This is primarily the oxides left over from burning coal (mixture of clay, quartz, glass, etc.). Sometimes, a blowing agent is used to reduce density and obtain a low density, oxide-based aggregate.

BRIEF SUMMARY OF THE INVENTION

[0016] A lightweight carbon aggregate concrete composition is disclosed as having between 15 - 50 wt % cementitious materials, such as Portland cement, and between 5 - 25 wt % water, and a lightweight carbon aggregate comprising between 10 - 30 wt % fine aggregate and between 15 - 35 wt % coarse aggregate, and between 0 - 0.4 wt % high-range water reducer. The lightweight carbon aggregate can be a mixture of bitumen, anthracite, waste coal, lignite, and combinations thereof. The cementitious materials react with the water and the lightweight carbon aggregate, which acts as a reducing agent in a reduction/oxidation reaction to generate a foaming gas that expands the composition as tire cement and w ater bind the composition, thereby forming a lightweight concrete having a specific tensile strength/density ratio in the range of 2.0 to 4.5 pounds per square inch (psi) /pounds per cubic foot (pcf).

[0017] Also disclosed is a method for producing a lightweight carbon aggregate concrete, comprising the steps of mixing a lightweight carbon aggregate comprising between 10 - 30 wt % fine aggregate and between 15 - 35 wt % coarse aggregate w ith a cementitious material, high range w ater reducer, and water. Then reacting the cementitious material with the water and the lightw eight carbon aggregate, which acts as a reducing agent in a reduction/oxidation reaction to generate a foaming gas that expands the concrete as the cementitious materials bind it, thereby forming a lightweight concrete having a specific tensile strength/density ratio in the range of 2.0 to 4.5 pounds per square inch (psi) /pounds per cubic foot (pcf). The lightweight carbon aggregate comprises a mixture of bitumen, anthracite, waste coal, lignite, and combinations thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Fig. 1 is a photograph of a pelletized coal mixture of fine aggregates and coarse aggregates;

[0019] Fig. 2 is a photograph of a cross-section of concrete containing lightweight carbon aggregate of the instant invention;

[0020] Fig. 3 is a graph of apparent density of rounded individual carbon aggregates vs. pelletized aggregate diameter;

[0021] Fig. 4 is a table of densities for various mesh splits of pelletized carbon aggregate;

[0022] Fig. 5 is a Weibull analysis demonstrating the strength behavior of carbon aggregate;

[0023] Fig. 6 is selected properties of a lightweight aggregate concrete composition example using the instant invention;

[0024] Fig. 7 illustrates typical properties for structural and moderate strength lightweight concrete;

[0025] Fig. 8 illustrates how gas generation causes the concrete to expand in its mold;

[0026] Fig. 9 shows the redox potential of two samples as a function of time when measured with a Danoplus Model Number ORP-100 Oxidation-Reduction Potential meter; [0027] Fig. 10 illustrates how a concrete cylinder is split to test tensile strength of lightweight concrete made using either carbon aggregate or pumice;

[0028] Fig. 11 is a graph of the tensile strength versus density of lightweight concrete using either carbon aggregate or pumice and depicts a tensile strength/density ratio;

[0029] Fig. 12 is a table showing components of lightweight concrete formed by carbon aggregate and the conventional formulation produced using pumice aggregate;

[0030] Fig. 13 is a comparison of both concrete formulations used in Fig. 12.

DETAILED DESCRIPTION OF THE INVENTION

[0031] Some embodiments of the present invention are described in this section in detail sufficient for one skilled in the art to practice the present invention without undue experimentation. It is to be understood, however, that the fact that a limited number of preferred embodiments are described does not in any way limit the scope of the present invention as set forth in the claims.

[0032] It is to be understood that whenever a range of values is described herein, i.e. , whether in this section or any other part of this patent document, tire range includes the end points and every point there between as if each and every such point had been expressly described. Unless otherwise stated, the words “about” and “substantially” as used herein are to be construed as meaning die normal measuring and/or fabrication limitations related to the value or condition which the word “about” or “substantially” modifies. Unless expressly- stated otherwise, the term “embodiment” is used herein to mean an embodiment of the present invention.

[0033] Coal, including waste coal that is too fine to be utilized in a power plant, also known as waste coal fines, can be used to create a vitreous carbon aggregate when fired to high temperatures in the absence of oxy gen. In the process, raw coal is first pulverized and tiren pelletized using binder in either a fluidized bed or a drum (or pan) granulation process; if waste coal is utilized, die pulverization process may be skipped. The aggregates are then fired under an inert gas: the oxygen and hy drogen in the coal leave during the process, but the carbon remains behind, continuing to crosslink and densify. Gases diat evolve from the coal during the thermal processing at a point when the coal is in a partial molten state can create stable bubbles in the structure, forming a carbon foam. If the reaction rate is controlled along with the amount of liquid phase formation and viscosity of that liquid, a porous, relatively strong, vitreous carbon aggregate is produced. Thus, the aggregate size can be controlled tiirough the forming process and the aggregate porosity can be controlled by varying tire ty pe of coal used and managing reaction rates and liquid formation in die firing process. This novel product has certain properties that set it apart from other conventional, low-density aggregates: 1) die density of solid vitreous carbon can be only as high as about 1.6 g/cm³. This is much lighter dian the density of more common silicates and aluminosilicates that make up expanded clay, shale, and pumice, which are closer to 2.6 g/cm³, 2) the vitreous carbon is quite strong and has good resistance to friability, unlike some of the weaker and more irregularly shaped aggregates like pumice, 3) any danger of alkali silica reaction is eliminated given its composition is primarily carbon, 4) selection of aggregate size for a given mix design could be easily provided through its forming process, thus, internal curing water can be delivered at die desired location and scale diroughout the concrete microstructure, and 5) vitreous carbon is relatively non-weting to water (wetting angle close to 90°). whereas all other conventional lightweight aggregates are weting. This could provide several advantages such as: a) once water is forced into the structure under light hydraulic pressure, it would not tend to leach out before use, i.e., water would tend to exist as disconnected pockets witiiin the pore structure with conventional aggregate, piles of lightweight aggregate must be constantly watered and turned, as the aggregate on the botom of the piles tend to carry more water than those on tire top due to flow of water and drainage, and this feature of carbon aggregate may lessen this effect; b) the permeability of lightweight concrete made with carbon aggregate would tend to be less given water would be inhibited from flowing through the aggregate, unlike most aluminosilicate based aggregates; c) water for internal curing would tend to migrate from the carbon aggregate at later times, which would benefit cement hydration at longer times; d) chemicals carried by water infused into carbon aggregate would be released over longer time periods, thus, reactants that could reduce permeability, such as viscosity enhancing or crack healing agents, may show improved performance; and e) dry ing shrinkage would be reduced given the menisci in fine pores within the aggregate would not convey stresses on tire matrix.

[0034] Target aggregate sizes can range from less than 0.5 nmi to over 10 mm in diameter. Some functions similar to those above might also be attained in asphalt-based products, proppants, fillers for plastics, and carbon-bearing magnesia refractories designed for improved resistance to slag attack and thermal shock resistance in steel processing applications; for example, pitch may better wet the surface of a carbon aggregate versus an oxide-based aggregate, possibly enhancing the properties of the asphalt. Coal, which is primarily a mixture of organic polymers, can be converted to lightweight vitreous carbon aggregates at atmospheric pressure using the methods of the instant invention. Densities can be similar to many other lightweight aggregates, however, lightweight carbon aggregates mixtures made from coal, herein referred to as a coal mixture, are newly taught with noted benefits.

[0035] The starting material coal may include bitumen, anthracite, waste coal, or even lignite, or blends of these coals that exhibit a ‘Tree swell index” as determined by ASTM D720 of betw een about 3.5 and about 5.0, but are preferably bituminous, agglomerating coals that have been comminuted to an appropriate particle size, preferably to a fine pow der below' about -60 to -80 mesh. Additionally, according to further highly preferred embodiments of tire present invention, tire coal starting materials of the present invention possess all or at least some of tire following characteristics: 1) a volatile matter content (dry, ash-free basis) of between about 35% and about 45% as defined by ASTM D3175, “Test Method for Volatile Matter in the Analysis of Coal and Coke”; 2) a fixed carbon (dry basis) between about 50% and about 60% as defined by ASTM D3172, “Practice for Proximate Analysis of Coal and Coke”; 3) a Gieseler initial softening temperature of between about 380°C and about 400°C as determined by ASTM D2639, Test Method for Plastic Properties of Coal by the Constant- Torque Gieseler Plastometer”; 4) a plastic temperature range above about 50°C as determined by ASTM D2639; 5) a maximum fluidity of at least 300 ddpm (dial divisions per minute) and preferably greater tiian about 2000 ddpm as detennined by ASTM D2639; 6) expansion greater dran about 20% and preferably greater dian about 100% as detennined by Amu Dilatation; 7) vitrinite reflectance in the range of from about 0.80 to about 0.95 as determined by ASTM D2798, ‘“Test Method for Microscopical Determination of the Reflectance of Vitrinite in Polished Specimens of Coaf’; 8) less than about 30% inert maceral material such as semifusinite, micrinite, fusinite, and mineral matter as determined by ASTM D2798; and 9) no significant oxidation of the coal (0.0 vol % moderate or severe oxidation) as determined by ASTM D 2798 and non-maceral analysis. The low softening point (380-400°C) is important so that the material softens and is plastic before volatilization and coking occur. The large plastic working range or “plastic range’' is important in that it allows die coal to flow plastically while losing mass due to volatilization and coking. Vitrinite reflectance, fixed carbon content, and volatile matter content are important in classifying these coal starting materials as “high-volatile” bituminous coals that provide optimum results in tire process of the present invention.

[0036] Fig. 1 is a photograph of a pelletized coal mixture 10 of fine aggregates 12 and coarse aggregates 14. Aggregate sizes can vary depending on predetermined properties. Fig.

2 is a photograph of a cross-section of lightweight concrete 16 containing lightweight carbon aggregate of the instant invention. Fine aggregate 12 and coarse aggregate 14 arc set in die lightweight concrete 16 photograph.

[0037] Fig. 3 is a graph of carbon aggregate apparent density vs. pelletized aggregate diameter. As seen in Fig. 3. a significant increase in apparent density occurs at a pelletized aggregate diameter of below about 0.4 inches. Fig. 4 is a table of densities for various mesh splits of pelletized aggregate. Fig. 5 is a Weibull analysis demonstrating the strength behavior of carbon aggregate (pellet) in a diametral compression test. The compression test results indicate a failure mode change at about 24 pounds weight (shown as lbs in tire table and P in tire chart), which corresponds to In (P) of about 3.2 on tire horizontal (X) axis. This data can be used to avoid certain aggregate failure modes in concrete compositions made from tire aggregate.

[0038] Fig. 6 is selected properties of a lightweight aggregate concrete composition example using the instant invention. Fig. 7 illustrates typical properties for structural and moderate strength lightweight concrete.

[0039] A novel feature was discovered when employing this material in the manufacture of lightweight concrete. We discovered drat carbon aggregate, when manufactured as described above, will slowly generate gas when introduced to cement and water to form concrete. This gas generation causes the concrete to expand in its mold, as shown in Figure 8. This concrete was cast about 0.75" below the top of the steel mold, then through gas generation rose to a height slightly above the top of the mold. This represents a linear expansion of about 15% in the z-direction, as seen in Figure 8.

[0040] In order to determine if the cause of the gas generation is a redox reaction, samples of carbon aggregate were introduced to water having a slightly oxidized environment: one had a larger particle size of +3/8” and the other a finer particle size of - 30/+50 mesh. Figure 9 shows the redox potential of these two samples as a function of time when measured with a Danoplus Model Number ORP-100 Oxidation-Reduction Potential meter. As is shown, the redox potential of the water is driven significantly to the reducing side, reaching roughly -100 mV in both cases. The finer aggregate held a more strongly reduced environment for a longer period of time. This could be due to a greater surface area accessible to the water. The larger aggregate likely had a larger volume fraction of internal porosity versus the smaller aggregate, and thus a significant amount of surface area, but given water does not readily penetrate the surface of the carbon aggregate, this surface area may have been inaccessible to water.

[0041] The tensile strength of lightweight concrete made using either carbon aggregate or pumice was tested using the diametral cylinder split test, where a concrete cylinder is split as shown in Figure 10. The tensile strength of the lightweight concrete that was formed by carbon aggregate had a significantly better strength-to-density ratio (specific strength) than the conventional formulation produced using pumice aggregate, as shown in Figure 11. A comparison of both concrete formulations is provided in Figure 12. The slump on the pumice bearing concrete was 1.5”, whereas that for the carbon aggregate bearing concrete was 0.5”. [0042] Figure 13 is an image of the cross-section of lightweight concrete sample bearing pumice as compared to that for carbon aggregate. The ruler shows 1-mm increments.

Visible pores in tire carbon aggregate bearing matrix look to be in the 0. 1 to 1-mm range; it is possible smaller pores are present. Note the prevalence of pores in the cement matrix with a size of approximately 0. 1 to 1-mm. Given tire fact that the pores are homogeneously spread throughout the matrix, it suggests gas was definitely generated by the fine aggregate, and because of this fact, likely generated by the coarse aggregate. Also note the lack of cementitious products in the porosity of the larger aggregate, suggesting the mix water did not easily penetrate the pore structure. [0043] One common product used in the manufacture of lightweight concrete is pumice. This material has relatively low density, but can be highly irregular in shape, very friable, and highly variable. It tends to breakdown during tire concrete mixing processing, changing tire overall particle size distribution. This also limits tire amount of porosity available to the concrete for mass reduction, and low densities can be difficult to achieve.

[0044] Another common lightweight concrete product that falls into this category is Autoclaved Cellular Concrete, also known as Autoclave Aerated Concrete (AAC). In the manufacture of AAC, aluminum powder is added to the concrete so that it can react with the alkaline water to generate hydrogen gas through oxidation of the aluminum powder, something like the following:

[0045] 2A1 (s) + 3H₂O (1) AI2O3 (s) + 3H₂ (g) ( 1 )

[0046] AAC requires an industrial sized autoclave to be produced at large scale. Autoclave systems use a steam pressure process to harden the aerated concrete once it has been formed, typically over a period of 6-12 hours using a temperatine of about 190°C and pressure of 174 psi. The quartz sand within the mixture reacts with calcium hydroxide due to the immense pressure. Autoclave hardening ensures better strength of the aerated concrete than the non-autoclaved aerated concrete. Densities are typically between 19 and 63 pounds per cubic foot having compressive strengths between 300 and 1500 psi. Given tire large fraction of porosity, the thermal conductivity of this product is relatively low, in the range of 0. 15-0.20 W/111-K [4],

[0047] Aluminum powder is a relatively hazardous material with an NFPA rating of 3. When ignited, it produces a metal fire that can be difficult to extinguish. Its reaction rate in concrete may also be highly impacted by particle size and extent of oxidation on the particles, which in turn can impact the resultant density and properties of the final AAC product.

[0048] In the current embodiment using carbon aggregate, the redox reaction or reactions are likely similar to that shown in Equation 1, though likely driven by a reducing agent such as carbon or maybe sulfur (not aluminum) generating hydrogen gas or possibly hydrocarbon gases like methane (CHty or acetylene (C₂H₂). Note, no hydrogen sulfide odor was detected (which can be smelled at concentrations < 1 ppm), so it is thought the impact of sulfur might be small.

[0049] The redox reaction can likely be controlled to achieve specific mechanical and thermal properties or ranges of properties of the LWA concrete. Additives, as taught herein, can be selectively used in the concrete composition to enhance and/or reduce reactions of both reduction and oxidation. [0050] Ultimately, our infrastructure must be upgraded and continuously improved through better concrete design. Engineered carbon aggregate provides a novel opportunity to offer new concrete designs and enhance tire lifetime of infrastructure components.

[0051] A lightweight carbon aggregate can be produced with the following steps; pulverizing and drying coal into a fine coal powder or direct utilization of dried waste coal fines: blending the fine coal powder and at least one additive to form a coal mixture: pelletizing the coal mixture using a binder to make coal aggregate comprising fine aggregates and coarse aggregates; foaming the coal aggregate by heating to a temperature between 250°C and 500°C under an inert gas, such as nitrogen, at atmospheric pressure; and pyroprocessing the coal aggregate to a temperature between 750°C and 1240°C under an inert gas, such as nitrogen, at atmospheric pressure to form a vitreous lightw eight aggregate having an apparent density of less than 95 pounds per cubic foot. The coal mixture can contain bituminous coal, subbituminous coal, anthracite, lignite, and combinations of these coal types thereof. The coal aggregate can be formed in a granulator or fluidized bed.

[0052] The foaming step can further comprise adding a particulate pore stabilizer to the coal aggregate, wherein the particulate pore stabilizer can be carbon black, fine oxides of alumina, silica, boric acid, titania, aluminosilicate clay, kyanite, fine non-oxide powders of silicon carbide, metal powders, and mixtures thereof. An additional step can be performed in sintering the coal aggregate to form a sintered lightw eight carbon aggregate. Also, an additional step of pyroprocessing the coal aggregate to cause volatilization and entrapment of volatized gases in a melted liquid phase at atmospheric pressure can be performed. The at least one additive can be at least one polymeric additive.

[0053] The blending step can further adjust the addition of the at least one additive to influence at least one of the amount of liquid formed in the coal mixture at a given time, the viscosity of tire liquid formed in the coal mixture, the rate at w hich the at least one additive reacts and cross-links in the coal mixture to form a solid.

[0054] The non-w etting behavior of tire carbon aggregate can inhibit tire release of water from the aggregate during concrete mixing, which in turn can enable the release of w ater to unreacted cement in tire concrete matrix over a longer period of time, wherein internal curing is enabled.

[0055] The lightweight carbon aggregate can be first infused with water to enhance internal curing of the concrete at late hydration times without significantly affecting the mix water content at early stages. The at least one additive can be water infused into the aggregate, further having reactants to alter the cementitious hydration products, shrinkage cracking inhibitors, viscosity enhancers, crack-healing agents, carbonation agents, and mixtures thereof.

[0056] A concrete composition produced by tire methods taught herein can include mixing the lightweight carbon aggregate with water, and given the non-wetting properties of the vitreous carbon, inhibit the release of the water during the concrete mixing step. The water within the carbon aggregate is then slow ly released over a much longer period of time, thereby providing internal curing. Another concrete composition is wherein the lightweight carbon aggregate is first filled with water and other additives that can be released over a much longer period of time to improve the properties of the concrete, such as reactants that can alter the cementitious hydration products to improve permeability or strength, shrinkage cracking inhibitors, viscosity enhancers to reduce permeability’, crack-healing agents, carbonation agents, or similar.

[00 7] An example lightweight carbon aggregate concrete composition can comprise between 15 - 50 wt % of cementitious materials, such as Portland cement, between 5 - 25 wt % water, a lightweight carbon aggregate comprising between 10 - 30 wt % fine aggregate and between 15 - 35 wt % coarse aggregate, between 0 - 0.4 wt % high-range water reducer. The cement reacts with the water to bind with the lightweight carbon aggregate and form a lightweight concrete.

[0058] The lightweight carbon aggregate can be formed from a mixture of bitumen, anthracite, waste coal, lignite, and combinations of coal thereof. The concrete composition can comprise a fine aggregate that is less than 8 mesh size. Also, the fine aggregate can have a bulk density’ of betw een 45-60 pounds per cubic foot and an apparent density of between 75-95 pounds per cubic foot. The coarse aggregate can be between 0.25 - 1 inches in diameter and have a bulk density of between 25-45 pounds per cubic foot and an apparent density of between 55-75 pounds per cubic foot.

[0059] The concrete composition can have a compressive strength of at least 1000 psi after 28 days, and a tensile strength of at least 100 psi with an average density of between 70- 115 pounds per cubic foot. The concrete composition can further comprise fly ash, hollow fly ash, ground granulated blast furnace slag, metakaolin, silica fume, other mineral admixtures, and combinations thereof. The cement in the concrete can react with water to set and harden the concrete to form pavement, architectural structure, foundation, motorwa /road, overpass, parking structure, brick, block, wall, footing for gate, fence and pole, bridge, foundation, levee, dam, manufactured stone veneer, and combinations thereof. [0060] The lightweight carbon aggregate can also have a non-wetting characteristic configured to reduce the permeability and dry ing shrinkage of the lightw eight carbon aggregate concrete. The concrete composition can further comprise graphite configured to increase tire electrical conductivity’ and thermal conductivity of tire lightweight carbon aggregate. The electrical conductivity of lightweight carbon aggregate made from coal can be varied over several orders of magnitude by processing to different temperatures or incorporating or inducing the formation of graphite in the aggregate. Carbon aggregate will also not passivate and form a low conductivity oxide coating in the cement matrix like metals. This can improve concrete performance characteristics such as grounding, protection against lightning, eliminating static electricity, environmental heating, and radio frequency interference screening.

[0061] The thermal conductivity of lightweight carbon aggregate made from coal can be increased by as much as a couple orders of magnitude (0.2 W/m-K to as much as 25 W/m-K) by incorporating or inducing the formation of graphite in the aggregate. This property might benefit the performance of concrete by limiting the thermal stresses that may form across the concrete due to thermal gradients or accelerating deicing through the ability to transport heat to the surface of the concrete more quickly.

[0062] The cement in the concrete composition can react with water to set and harden the concrete to form pavement, architectural structure, foundation, motorway /road, overpass, parking structure, brick, block, wall, footing for gate, fence and pole, bridge, foundation, levee, dam. manufactured stone veneer, or combinations thereof. The permeability and drying shrinkage of the concrete can be reduced by the non-wetting characteristic of the vitreous carbon aggregate.

[0063] The foregoing explanations, descriptions, illustrations, examples, and discussions have been set forth to assist the reader with understanding this invention and further to demonstrate the utility and novelty of it and are by no means restrictive of the scope of tire invention. It is tire following claims, including all equivalents, which arc intended to define the scope of this invention.

Claims

CLAIMS:

1. A lightweight carbon aggregate concrete composition, comprising; between 15 - 50 wt % cementitious materials, such as Portland cement. between 5 - 25 wt % water, a lightweight carbon aggregate comprising between 10 - 30 wt % fine aggregate and between 15 - 35 wt % coarse aggregate, wherein the lightweight carbon aggregate comprises a mixhire of bitumen, anthracite, waste coal, lignite, and combinations thereof, and between 0 - 0.4 wt % high-range water reducer, wherein tire cementitious materials react with the water and the lightweight carbon aggregate using a reducing agent in a reduction/oxidation reaction to generate a foaming gas that expands and binds the composition, thereby forming a lightweight concrete having a specific tensile strength/density ratio in the range of 2.0 to 4.5 pounds per square inch (psi) /pounds per cubic foot (pcf).

2. The concrete composition of claim 1, wherein the fine aggregate is less than 8 mesh size.

3. The concrete composition of claim 1, wherein the fine aggregate bulk density is between 45-60 pounds per cubic foot and the apparent density is between 75-95 pounds per cubic foot.

4. The concrete composition of claim 1. wherein tire coarse aggregate is between 0.25 - 1 inches in diameter.

5. The concrete composition of claim 1, wherein the coarse aggregate bulk density is between 25-45 pounds per cubic foot and the apparent density is between 55-75 pounds per cubic foot.

6. The concrete composition of claim 1, wherein the lightweight carbon aggregate concrete compressive strength is at least 1000 psi after 28 days.

7. The concrete composition of claim 1. wherein tire lightweight carbon aggregate concrete tensile strength is at least 100 psi.

8. The concrete composition of claim 1, wherein the lightweight carbon aggregate concrete average density is between 70-115 pounds per cubic foot.

9. The concrete composition of claim 1, wherein the composition further comprises fly ash, hollow fly ash, ground granulated blast furnace slag, metakaolin, silica fume, other mineral admixtures, and combinations thereof.

10. The concrete composition of claim 1, wherein the cement is configured to react with water to set and harden the concrete to form at least one of pavement, architectural structure, foundation, motor ay /road, overpass, parking structure, brick, block, wall, footing for gate, fence and pole, bridge, foundation, levee, dam, manufactured stone veneer, and combinations thereof.

11. The concrete composition of claim 1, wherein tire lightweight carbon aggregate comprises a non-wetting characteristic configured to reduce the permeability of the lightweight carbon aggregate concrete.

12. The concrete composition of claim 1 , wherein the lightweight carbon aggregate comprises a non-wetting characteristic configured to reduce drying shrinkage of the lightweight carbon aggregate concrete.

13. The concrete composition of claim 1, further comprising graphite configured to increase the electrical conductivity of the lightweight carbon aggregate.

14. The concrete composition of claim 1. further comprising graphite configured to increase the thermal conductivity of the lightweight carbon aggregate.

15. The concrete composition of claim 1, wherein the reducing agent is at least one of carbon, sulfur, and mixtures thereof

16. A method for producing a lightweight carbon aggregate concrete, comprising the steps: mixing a lightweight carbon aggregate comprising between 10 - 30 wt % fine aggregate and between 15 - 35 wt % coarse aggregate with a cementitious material, high range water reducer and water; and reacting the cementitious material with the water and the lightweight carbon aggregate, using a reducing agent in a reduction/oxidation reaction, to generate a foaming gas that expands and binds the concrete, thereby forming a lightweight concrete having a specific tensile strength/density ratio in the range of 2.0 to 4.5 pounds per square inch (psi) /pounds per cubic foot (pcf); wherein the lightweight carbon aggregate comprises a mixture of bitumen, anthracite, w aste coal, lignite, and combinations thereof.

17. The method of claim 16, further comprising the step: inhibiting the rate of adsorbed w ater released by the lightw eight carbon aggregate during the reacting step thereby providing internal curing.

18. The method of claim 17, wherein the lightweight aggregate is first filled with w ater and additives released over a longer period of time to improve concrete properties.

19. The method of claim 18, wherein the additives improve the lightweight carbon aggregate concrete by altering permeability, strength, shrinkage, cracking, viscosity, crack-healing, carbonation, and combinations thereof.

20. The method of claim 16, wherein; the fine aggregate bulk density is between 45-60 pounds per cubic foot and the apparent density is betw een 75-95 pounds per cubic foot, and the coarse aggregate bulk density is betw een 25-45 pounds per cubic foot and tire apparent density is between 55-75 pounds per cubic foot.